Lightweight metallic structure



Jan. 13, 1970 M. A. LEVINSTEIN LIGHTWEIGHT METALLIC STRUCTURE Filed Jan.5, 1967 I NVEN TOR.

3,489,534 LIGHTWEIGHT METALLIC STRUCTURE Moses A. Levinstein,Cincinnati, Ohio, assignor to General Electric Company, a corporation ofNew York Filed Jan. 3, 1967, Ser. No. 606,943 Int. Cl. B23k 31/00; B21f45/00; B21c 37/00 US. Cl. 29191.6 6 Claims ABSTRACT OF THE DISCLOSURE Alightweight metallic structure, such as a shroud, includes hollow wiresbonded together. The Wires are an alloy including at least one ofaluminum, magnesium or their alloys and at least one of iron, nickel,cobalt or their alloys.

This invention relates to lightweight metallic structures and, moreparticularly to such a structure including members such as filaments,strands or wires of metal bonded together.

Lightweight mesh, fabric or metal wool structures, hereafter calledmesh, employing strands, wires or filaments, hereafter called wires,held to or bonded with one another, alone or as a support for othermembers, use such wires in solid form in uniform or random arrangements.Such wires can be bonded together by welding, brazing and the like.

One use for such a structure is as a gas seal held between successivestages of an axial flow turbine. In such an application layers of meshbonded to holding members, are located opposite the tips of bladingmembers. In some applications filler materials are disposed betweenwires. Because of the variety of metals available for the wires andvariety of available filler or bonding material, abradbility,temperature resistance, oxidation resistance and the like can beselected for the mesh. However, because commerically avaiable fine wiresare solid, the density of the material is greater than that which wouldbe most desirable, particularly for use in an aircraft gas turbine whereweight is an important factor.

It is the principal object of the present invention to provide animproved lightweight metallic structure including layers of fine hollowwires or mesh to decrease the density of the structure.

Another object is to provide an improved, lightweight gas turbineabradable shroud.

These and other objects and advantages will be more clearly understoodfrom the following detailed description, examples and the drawing.

In the drawing:

FIG. 1 is a sectional isometric view of a wire having a solid metalliccore and a continuous metallic shell prior to processing;

FIG. 2 is a sectional isometric view of the wire of FIG. 1 afterprocessing;

FIG. 3 is a partially sectional isometric view of a shroud including thestructure of the present invention;

FIG. 4 is a more detailed sectional view of a shroud of the presentinvention including stacked unwoven wires; and

FIG. 5 is a sectional view of the upper portion of the shroud as shownin FIG. 4 with wires in the form of a mesh.

In order to attain and fulfill the above objects, a lightweight metallicstructure is made by providing a metallic wire or mesh core of a firstmetal and then coating it, such as by electro or vapor deposition, witha shell of a second metal to produce a composite Wire or mesh. Thecrystal relationship and relative diffusion rates between the core metaland the shell metal is such that the core metal will diffusepreferentially into the shell metal to United States Patent 0 3,489,534Patented Jan. 13, 1970 produce a wire or mesh having a hollow interiorbounded by the shell metal. This will occur when the composite wire ormesh is heated at a temperature below the melting point of the shellmetal and in the absence of a shellcrushing pressure. Metals which canbe used in this manner for a core material include aluminum, magnesiumand their alloys. Metals which can be used as the coating or shellmaterial include iron, nickel, cobalt and their alloys.

According to one form of the present invention, after a core wire iscoated, the composite wire thus formed can be arranged into a mesh orother desired configuration. A plurality of meshes or individual wirescan be stacked beside or one upon the other or both to provide whateverthickness is desired. Then the composite members are held in intimatecontact at various points along their surfaces and heated at thattemperature sufiicient to diffuse the core metal into the shell metalbut below the melting point of the shell metal. The result is alightweight porous structure comprising a plurality of wires or meshesbonded one to the other, each wire or mesh having a hollow core. If morerigidity, ductility, bonding or body is desired, solid wires or powderedfiller material such as brazing alloys or both can be intermixed orinterwoven with the composite wires or meshes.

Described in co-pending application Ser. No. 606,963, filed Jan. 3, 1967and assigned to the same assignee as this invention is a method formaking hollow members which includes the making of hollow wires, meshesand tubes. It has been found that if, during heating to diffuse the coremetal into the shell metal, a plurality of composite wires or meshes aremaintained in contact under sufficient pressure to maintain the contatbut not sufiicient to cause collapse of walls of the hollow wiresproduced, the wires not only can be made hollow but also can be bondedinto a more rigid structure.

Referring to the drawing, the isometric sectional view of FIG. 1 shows acomposite wire 10 having a core 11 most conveniently and preferably of ametal of the group aluminum, magnesium and their alloys. Surrounding thecore is a coating or shell 12 of a metal into which core 11 will diffuseupon heating to a temperature such as above the melting point of core11. Most desirable shell metals for this purpose are metals of the groupof iron, cobalt, nickel and their alloys.

After heat treatment according to the present invention, such as aboutan hour at 2000 F., core 11 of the composite wire 10 in FIG. 1 diffusesinto shell 12 to form an alloy 14 as shown in FIG. 2. When such a metalas aluminum is used for the core and nickel for the shell, it has beenfound that original composite Wire outside diameter d in FIG. 1increases to hollow wire outside diameter D in FIG. 2. If a plurality ofstacked mesh including composite wires is contained in a fixed volumeduring heat treatment, such increase in diameter produces a slightpressure between the wires. This assists in bonding together duringprocessing the plurality of composite wires. Therefore, a holding orconfining structure in which the plurality of wires or meshes are placedcan be shaped to provide a desired arrangement.

One such arrangement which can be made is shown in FIG. 3 during thepractice of the method of this invention. A sectional view of theproduct is shown in FIG. 4. Referring to those two figures, a shroudbacking member 16 of a stator portion of an axial flow turbine, for useopposite rotating blades, was placed on a fixture base 18 having acurved surface 20 adapted to receive the shroud member. A nickel basebrazing alloy powder 22, in the form of a paste or slurry, was placed onthe exposed surface of shroud member 16. Solid wires of a nickel basealloy 24, sometimes referred to as Nichrome alloy, were placed over thebrazing alloy 22. In another example substantially pure nickel wire meshwas used.

Composite wires 26 made of 15-40 mil aluminum wire as the core with a5-10 mil thick coating of nickel as the shell were then placed on thesolid wires 24. By weight, this consisted of 2027% Al and 73-80% Ni. Asshown in FIG. 5, the wires can be partially or entirely woven togetherinto a mesh. A top holding plate 28 was placed on the stackedwire-brazing alloy combination. In order to assure bonding of thevarious wires and brazing alloys together and to the shroudbackingmember 16, a slight holding pressure, represented by arrow 30, wasapplied to the stacked wires through holding .plate 28. For example,this can be accomplished by clamping strips or other clamping means wellknown in the art..

However, the pressure applied should be less than that which would causecollapse of the hollow wire during or after processing.

The clamped structure was then heated for one hour.

at about 2000 F. in argon to diffuse the aluminum core 11 into shell 12to form a shell 14 of a nickel-aluminum alloy as shown in FIGS. 1 and 2.This produced hollow wires 26 of FIG. 4 or FIG. 5. At the same time, theheat treatment bonded wires 26 together and to wire mesh or structure 24and also brazed solid wires 24 to shroud 16 to form'the abradable shroudshown in FIG. 4.

In another specific example, 25 mil aluminum wires were first coatedwith 7.5 mils of nickel by electroplating. The nickel-aluminum alloy 14in FIG, 2 was produced after diffusion of thealuminum wire into thenickel shell in an argon atmosphere furnace in which the temperature wasincreased over a period of about 2 hours from room temperature to 2000F. The material was then held for /2 hour at 2000 F. after which it wasslowly cooled over a period of about 1 hour. The relatively slow heat upperiod or rate is desirable to avoid rupture of the shell wall as aresult of too rapid a diffusion and expansion.

However, frequently in the manufacture of shroulds as described above,some incidence of shell wall rupture in the tubular structure can betolerated: the density is not appreciably increased and the highporosity and void space through a very high percentage of the remainderof the tubes and structure provides the material with suitable;

abradibility.

In one example, a 99% aluminum core in the form of a 120 X 120 mesh of 4mil wire in a twill weave first was coated as a unit with 1.5 mils ofnickel in an electroplat-' ing bath. Such coating by electroplating orvapor deposition can be accomplished readily with well known processeshaving suflicient throwing power to deposit nickel over virtually theentire exposed surface. By moving the electroplating holder from time totime during plating,

a substantially completely coated composits structure can be produced.Then upon heating to diffuse the core into 4 structure of the'finalhollow tubular member is to be specifically avoided, then the core wiresshould be coated individually prior to their being woven or grouped intoa mesh, fabric, metal wool and the like.

It has been found that composite wires having a core consistingessentially of 5-35 weight percent of the composite wire are preferredfor use in the present invention.

' Below about 5%, too small a void is created because of meant to betypical of the invention rather than any limitation. It is intended bythe appended claims to cover the various modifications and variations ofwhich the invention is capable within the knowledge of one skilled I inthe art.

What is claimed is: 1. An improved lightweight metallic structurecompris ing:

a plurality of hollow wires bonded together; the hollow wires being analloy of at least one element selected from the group consisting of Al,Mg and their alloys and at least one element selected from the groupconsisting of Fe, Ni, Co and their alloys; the structure having athickness of a plurality of hollow wires. 2. The structure of claim 1 inwhich a plurality of solid wire members are bonded with the hollowwires.

3. The structure of claim 2 in which there is at least one layer ofwires in the form of a mesh.

4; Animproved lightweight shroud comprising: a backing member; and

a plurality of layers of hollow wires bonded together into the backingmember;

. the hollow wires being an alloy of at least one element selected fromthe group consisting of Al, Mg and their alloys and at least one elementselected from the group consisting of Fe, Ni, Co and their alloys.

5. The shroud of claim 4 in which a plurality of solid wire members arebonded with the hollow wires.

6. The shroud of claim 5 in which at least one of the 1 layers of wiresis in the form of a mesh.

References Cited UNITED STATES PATENTS 2,271,662 2/1942 Rubissow 2101693,087,233 4/1963 Turnbull 29-182 3,123,446 3/1964- Wheeler 29-1833,266,130 8/1966 Glaze 29-163.5

L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant ExaminerUS. Cl. X.R.

